I have made a function in C to calculate large numbers for my future project,

because with the average calculators it's an impossible task.

Is that function working properly?

I would like to know that how far am I from the correct sum.

Factorial

65536! = 5.162948523097533 e +287193

Power

65536 ^ 65536 = 6.741140125499081 e +315652

Thank you!